Apparatus and method for making a photoconductive element



2,659,682 zms M N E 00 m Emw DT Mum c m Nov. 17, 1953 N APPARATUS A PHO'I 2 Sheets-Sheet 1 Filed Aug. 5, 1948 f. If

NDRMAN E. ANDERSON Nov. 17, 1953 C ANDERSON 2,659,682

APPARATUS AND METHOD FOR MAKING A PHOTOCONDUCTIVE ELEMENT Filed Aug. 5, L948 2 Sheets-Sheet 2 #1 4 '11 m E 1 m L5 2 m I:

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u R I m U F l 8 5 swam M NURMAN [l ANDERSON wag Patented Nov. 17, 1953 APPARATUS AND METHOD FOR MAKING A PHOTOCONDUCTIVE ELEItIENT Norman C. Anderson, Batavia, Ill., asslgnor to Continental Electric Company, Geneva, 11]., a

corporation of Delaware Application August 5, 1948, Serial No. 42,679

' 7 Claims. (01. 117-97) This invention relates to improvements in photo-electric cells, particularly of the photoconductive type.

It has been proposed heretofore to provide photo-electric cells using lead sulphide for the conductive elements, but such proposals have not been entirely satisfactory due to dimc'ulties of forming the cells.

The object of this invention'is to improve the construction and method of making photoelectric cells of the photoco'nductive type byproviding for the manufacture of such cells with favorable characteristics in great quantities uhdercontrolled conditions.

One embodiment of the process of this invention, and the apparatus used in connection therewith, is illustrated in the accompanying drawings, in which:

Fig. l is a perspective view of the photo-electric cell made in accordance with this invention;

Fig. 2 is a sectiona1 view through the exhaust and activation device for the cell; and

Fig. 3 is a diagrammatic view of the exhaust system.

In the copending application of Gerhard Lewin and John Benes, Jr., for Photo-Electric Tubes, Serial No. 743,040, iiied April 22, 1947 and now Patent No. 2,537,225, is set forth a process of making a photo-electric cell. This method consistedof cutting a piece of glass tubing to length, making a press on one end of the glass tube with two protruding rigid lead wires forming the electric conductors for the photo-sensitive surface and located on the outside of the press, depositing the photo-sensitive material on the inside of the tube, sealing on of anexhaust tube to the other end of the glass tube, and, activating and exhausting said photo-electric material.

This invention utilizes the principle there described and has reference particularly to the method of depositing and activating a photo sensitive surface on the inside of the tube, with reference especially to the photoconductive type of surface.

In this type of surface the resistance of a semi-conductive material is reversibly changed b impinging radiation; Materials having this property are well-known and particularly compounds of the group comprising lead, thallium, and silver in combination with one or more of the group comprising oxygen, sulphur, selenium, and tellurium show the desired properties. While the process is described in connection with photo-electric cells having a sensitive surface composed of lead, sulphur and oxygen, it will be understood that the same process can be applied to other materials mentioned above.

Referring to Fig. 1, the cells comprises an envelope or tube generally designated at I,initially formed of a glass cylinder, preferably made of lime or lead glass. The tube I is provided with a press 2, on'one end thereof, which seals said end and also seals thelead-in connections or conductors for the tube, Extending into the lower end of the press 2, are two or more conductors 3, composed of an outer lead, preferably of nickel, and an intermediate wire or piece of metal designated at I, having the same expansion plied to each termina1 on the inside wall of the tube I, adjacent the conductors 4, to which the latter are connected. It is preferred to use a silver paint combined with a binder and havin good conductivity, which binder usually is composed 'of 'an organic;compound which will bake out at a relatively low temperature and thus be, decomposed. I have found that a. silver paint sold under the trade name Dupont No. 4810, has the property of baking out at a temperature of 300 C. and to be very suitable for this purpose.

Next a suitable conductive material, such as carbon or platinum is applied in the form of a strip 6, on opposite sides, or diflerent sides, to the inside wall of the tube I. This material may be applied by a ruling pen and extends from the paste of silver paint 5, with which it is in contact, to the photo-sensitive surface I on the inside of the tube I. The tube is then submitted to a baking process, and when aquadag is used by a gradual increase in temperature to 300 C as the electrode material, this is accomplished An exhaust tube 8 is then sealed onto the outer end of the tube I, and the cell is thus prepared aesaoee 25 C. for approximately fifteen minutes. Quartz cylinders which have been previously thoroughly cleaned by immersion in dilute hydrofluoric acid and subsequent heating, are introduced in the solution on a suitable holder immediately after mixing. After deposition of a coating the cylinders are dried in air and the procedure is repeated until a coating of suitable thickness has been obtained, which is, in averagefthe case after three treatments. The cylinders are heated in air at a temperature between 120 C. and 700 C., and are ready for further operation.

This step of manufacturing can be modified by the use of cylinders on which the material instead of being chemically deposited has been evaporated from natural galena or chemical lead sulfide at temperatures of approximately 400 C. on cylinders and air pressure of approximately 200 microns. It is to be here understood that suitable compounds of other semi-conductive material containing thallium, silver, oxygen, selenium, tellurium and the like may be substituted for the thioreau and lead acetate.

A cylinder as thus prepared is designated generally at 9, in Fig. 2, with the coating thereon designated It). This cylinder is shown as mounted over a heating coil H, preferably formed of platinum or other good conductor, and connected through terminals It, to a source of electric supply which can be regulated by a resistor or a variac, the voltage being indicated on a voltmeter The prepared blank is slipped over the refractory cylinder 9, with the deposited material l thereon, so that the terminals of the conducting strips are opposite the cylinder. The outer end of the exhaust tube 8. has a vacuum-tight contact with a piece of cushion material capable of withstanding high temperatures, such as silicone rubber indicated at It, so the inside of the tube can be evacuated through a manifold generally indicated in Fig. 3, at I5, by a vacuum pump IS. The manifold l 5 may be provided with a stop cock l1, and a connection It, adapted to extend to a vacuum gauge, and also may have an additional connection I 9, to extend to a Pirani gauge.

As indicated in Fig. 3, a plurality of blanks may be treated simultaneously, all of which are mounted in side-by-slde relation on a support generally designated at 20, forming a cover over a hood 2|, connected with the exhaust manifold l5 through a tube 22.

A plate 23 is also connected with the support 20, and carries upstanding rods 24 upon which is slidably mounted a heating oven generally designated at 25. This forms a practical method of treating a considerable number of blanks simultaneously, thereby facilitating the manufacture of the cells. The oven 25 contains a heating coil 26 therein, adapted to be connected through a power line 21 to a source of electric supply.

This oven preferably is made of glass or other transparent material, so as to observe the treatment of the blanks.

When the oven has been lowered over the blanks, temperature therein is raised by a coil 26 to approximately 250 C.-450 0., and the quartz. cylinders 9 are heated progressively by electric current passing through the heaters ll until the material l0, deposited on the cylinders 9, starts to evaporate. A variable leak 28 has been opened by a stop cock in the manifold I5, and air pressure in the system is read on a vacuum gauge connected therewith. This air pressure should be between 1 and 60 mm. oi mercury. The evaporation continues until approximately all of the photo-sensitive material has been deposited at 1 on the inside wall of the tube I. as may be determined by observation.

After the sensitive material has been deposited, the oven 25 is raised, and the cells are cooled to room temperature. The manifold is is shut off from the vacuum pump 16; air is introduced into the system; and the cell or cells can be removed from the individual seats I d.

The tubes are then introduced to another manifold where they are exhausted to a pressure below microns of air and the exhaust tubes 8 are sealed off, and the tube is then sealed at 29. thus making the cell a vacuum-tight cell device. This last procedure may be omitted on certain types of cells by sealing off tubes at gas pressures up to atmospheric pressure if desired.

The process described allows for the manufacture of photoelectric cells with favorable characteristics in great quantities under controlled conditions.

While the invention has been illustrated and described in one embodiment, it is recognized that variations and changes may be made therein, without departing from the invention, except as specified in the claims.

I claim:

1. In apparatus for manufacturing a photoconductive cell, the combination of a support having an upstanding support thereon adapted to receive a layer of semi-conductive material thereon, a cushion surrounding the upstanding support in position for sealing engagement with an exhaust tube on an envelope, upstanding guides carried by the first-mentioned support, an oven slidablymounted on the guides for lowering movement over the envelope, and heating means in the upstanding support.

2. In apparatus for manufacturing a photoconductive cell, the combination of a support having an upstanding support thereon adapted to receive a layer of semi-conductive material thereon, upstanding guides carried by the first mentioned support, an oven slidably mounted on the guides for lowering movement over the envelope, and heating means in the oven for heating the material on the support.

3. In apparatus for manufacturing a photo.- conductive cell, the combination of a support having an upstanding support thereon adapted to receive a layer of semi-conductive material thereon, a cushion surrounding the upstanding support in position for sealing engagement with an exhaust tube on an envelope, upstanding guides carried by the first-mentioned support. an oven slidably mounted on the guides for lowering movement over the envelope. and means in the oven for heating the material on' the support.

4. A method of making a photo-conductive tube included an envelope, comprising depositing a layer of lead sulphide on a supporting surface, introducing the lead sulphide on said surface into the envelope, and transferring the lead sulphide by evaporation from the surface onto the envelope while activating said lead sulphide by heating said surface to a temperature between 250 Grand 450 C.

5. A method of making a photo-conductive tube including an envelope, comprising depositing a layer of lead sulphide on a supporting surface, introducing the lead sulphide on said surface into the envelope, and transferring the lead sulphide by evaporation from the surface onto the envelope while activating said lead sulphide by heating said surface to a temperature between 250 C. and 450 C. in an atmosphere of between 1 and 60 mm. of mercury.

6. In apparatus for manufacturing a photoconductive cell, the combination of a cylindrical support adapted to receive a layer of semi-conductive material thereon and to have the cell telescoped thereover, an electric heating element within the cylindrical support for evaporating the material therefrom onto the cell, and an oven for heating the cell. A

7. In apparatus for manufacturing a, photoconductive cell, the combination of a cylindrical support adapted to receive a layer of semi-conductive material thereon and to have the cell telescoped thereover, an electric heating element within the cylindrical support for evaporating the material therefrom onto the cell, means for supporting the cell over the support, an oven for surrounding the cell, and heating means in the oven.

NORMAN C. ANDERSON.

References Cited in the file of this patent UNITED STATES PATENTS 

4. A METHOD OF MAKING A PHOTO-CONDUCTIVE TUBE INCLUDED AN ENVELOPE, COMPRISING DEPOSITING A LAYER OF LEAD SULPHIDE ON A SUPPORTING SURFACE, INTRODUCING THE LEAD SULPHIDE ON SAID SURFACE INTO THE ENVELOPE, AND TRANSFERRING THE LEAD SULPHIDE BY EVAPORATION FROM THE SURFACE ONTO THE ENVELOPE WHILE ACTIVATING SAID LEAD SULPHIDE BY 